In recent years, various techniques have been suggested to automate the detection of a fluorescently-labeled sample. For example, Japanese Patent Unexamined Publication No. 2001-238674 suggests a DNA disk using an existing optical disk technique. According to this technique, a series of spots are formed to be arranged on the disk in a spiral manner and a track is formed along the arranged spots and an address mark is formed on this track. Light is scanned along the track and the fluorescence generated from the spot due to this light is detected by a light detector.
Japanese Patent Unexamined Publication No. 2001-238674 also discloses a configuration to remove fluorescence generated at a region other than the spot (so-called outside-region fluorescence or autofluorescence). When light passes through a disk substrate or other optical members for example, the outside-region fluorescence or autofluorescence occurs. When such autofluorescence enters a light detector, a risk is caused where a lowered accuracy is caused to detect the fluorescence generated from a sample existing in the spot. In order to suppress such a disadvantage, Japanese Patent Unexamined Publication No. 2001-238674 discloses a configuration in which an aperture is placed in a front stage of the light detector to converge the fluorescence generated due to the sample at an opening section of the aperture to thereby remove unnecessary fluorescence such as outside-region fluorescence or autofluorescence.